IO0Oo NEW YORK STATE MUSEUM 
brachiopods (Orthis elegantula, etc.) and the so called Oster- 
garn beds which still contain Eurypterus, but also Lucina (Ilionia) 
prisca, Meristina didyma, Leperditia and in their upper- 
most layers species of Chonetes, Spirifer, Beyrichia, etc. 
Thus the Eurypterus beds of the Salina formation in which the 
fauna reaches its climacteric development, are clearly stamped with their 
marine origin, and the. profusion and perfection of preservation of the 
eurypterid remains precludes the possibility of their transportation into 
the basin by land waters; it is also apparent that the beds were not formed 
under normal marine conditions. The eurypterid horizons of Kokomo, of 
the Salina and of Oesel, as well as of Great Britain, exhibit as clearly 
all the characteristics of a particular and peculiar marine facies, as do the 
graptolites or the corals. These facies are indicated partly by the unusual 
nature of the rocks and partly by the peculiar aspect of the associated 
lowed after an interval by several hundred feet of shales and sandstones that form 
the top of the Frankfort formation and contain a distinct fauna without eurypterids. 
These rocks, elsewhere designated the Indian Ladder beds, are typically exposed in a 
high bluff below the Indian Ladder at the Helderberg escarpment. 
The peculiar restriction of the eurypterids to the easternmost exposures of the 
Frankfort shale would seem at first to be explicable, as in the case of the Salina faunas, 
by assuming their occurrence in “pools.” But the Frankfort shale exhibits 
notable differences from the Salina in total thickness, faunal association and 
lithological character as between the eastern and western occurrences, evidence which 
tends to indicate that the eastern beds were deposited close to the shore line, and the 
more western beds farther offshore. The Frankfort eurypterids were thus inhabitants 
of the shallow littoral waters with their mud flats and lagoons, and if the shore line of 
the late Utica-Frankfort period extended in northeast-southwest direction, just east 
of the lower Mohawk‘ region, as conceived by Schuchert [Paleogeography of North 
America, pl. 60] the exposures along the lower Mohawk valley happen to intersect only 
their former narrow habitat. The range of the eurypterids extends in this limited area 
through a thickness of from 1500 to 2000 feet which is due to the fact that this region 
was apparently involved in the Appalachian folding then going on, and thereby suffered 
depression while large quantities of material were swept down from the rising land 
in the east. 
